Field of the Invention
The present invention relates to a fabricating method of a unit structure materializing an electrode assembly fabricated by a stacking method other than a folding method, a fabricating method of the electrode assembly and an electrochemical cell including the electrode assembly.
Description of the Related Art
A secondary battery attracts attention as a power source of an electric vehicle (EV), a hybrid electric vehicle (HEV), a parallel hybrid electric vehicle (PHEV), and the like, which have been suggested as alternatives for solving defects such as environmental contamination due to commonly used gasoline vehicles, diesel vehicles, and the like using fossil fuels. In a medium and large size device such as automobiles, a medium and large size battery module in which a plurality of battery cells is electrically connected is used due to the need of high power and high capacity.
However, since the medium and large size battery module is necessary to be manufactured so as to have a small size and a light weight, a square shape battery, a pouch shape battery, and the like, which may be stacked in a high degree and have a light weight when compared with the capacity, are widely used as the battery cells of the medium and large size battery module.
In the case of the battery cell, an electrode assembly is included. Generally, the electrode assembly is classified according to the structure of the electrode assembly including a cathode/separator/anode structure.
Typically, the electrode assembly may be classified into a jelly-roll (a wrapping type) electrode assembly, in which cathodes and anodes having long sheet shapes along with an interposed separator are wrapped, a stack type (a laminated type) electrode assembly, in which a plurality of cathodes and anodes along with interposed separators, which are cut into specific size units, are stacked one by one, and a stack/folding type electrode assembly.
First, the stack/folding type electrode assembly disclosed in Korean Patent Application Publication Nos. 2001-0082059 and 2001-0082060 filed by the present Applicant will be explained.
Referring to FIG. 1, an electrode assembly 1 of a stack/folding structure includes a plurality of overlapped full cells 2, 3, 4 . . . (Hereinafter, will be referred to as full cell) as unit cells, in which cathode/separator/anode are positioned in sequence. In each of the overlapped parts, a separator sheet 5 is interposed. The separator sheet 5 has a unit length possibly wrapping the full cells. The separator sheet 5 initiated from the central full cell 1b is bent inward by the unit length while continuously wrapping each of the full cells to the outermost full cell 4 so as to be interposed in the overlapped parts of the full cells. The distal portion of the separator sheet 5 is finished by conducting heat welding or attaching using an adhesion tape 6. The stack/folding type electrode assembly is manufactured by, for example, arranging the full cells 2, 3, 4 . . . on the separator sheet 5 having a long length and wrapping from one distal portion of the separator sheet 5 in sequence. However, in this structure, a temperature gradient may be generated between the electrode assemblies 1a, 1b and 2 in the center portion and the electrode assemblies 3 and 4 disposed at the outer portion to produce different heat emitting efficiency. Thus, the lifetime of the electrode assembly may be decreased when used for a long time.
The manufacturing process of the electrode assembly is conducted by using two lamination apparatuses for manufacturing each electrode assembly and one additional folding apparatus as a separate apparatus. Therefore, the decrease of the tack time of the manufacturing process has a limitation. Particularly, the minute aligning of the electrode assemblies disposed up and down is difficult in the structure accomplishing the stacked structure through the folding. Thus, the manufacture of an assembly having a reliable quality is very difficult.
FIG. 2 illustrates A type and C type bicell structures which are unit structures applicable instead of the full cell in the electrode assembly of the above-described stack/folding type structure in FIG. 1. At the center portion of the electrode assembly of the stack/folding structure, which is the initiating point of wrapping, a bicell (‘A-type bicell’) having (a) a cathode/separator/anode/separator/cathode structure or a bicell (‘C-type bicell’) having (b) an anode/separator/cathode/separator/anode structure, wrapped with a separator sheet may be disposed.
That is, the common bicell may have a structure of the ‘A-type bicell’ having a stacked structure of a double side cathode 10, a separator 20, a double side anode 30, a separator 40 and a double side cathode 50 one by one as illustrated in FIG. 2(a), or the ‘C-type bicell’ having a stacked structure of a double side anode 30, a separator 20, a double side cathode 10, a separator 40 and a double side anode 60 one by one as illustrated in FIG. 2(b).
In the electrode assembly structure fabricated by applying the folding process, a folding apparatus may be separately necessary. When applying the bicell structure, the bicells may be fabricated by two types (that is, A-type and C-type) and stacked. Before conducting the folding, the keeping of accurate distance between the bicells disposed on a long separator sheet may be very difficult. That is, when conducting the folding, the accurate alignment of upper and lower unit cells (meaning the full cells or the bicells) may be difficult. In addition, when manufacturing a high capacity cell, considerable time may be necessary for changing the types.